Resilient accumulator reservoir with failure switch

ABSTRACT

A fluid accumulator reservoir including metallic conductors slidably embedded within the resilient walls defining the reservoir, the conductors being positioned to indicate whether a desired amount of fluid exists in the reservoir. When the reservoir is properly filled the resilient material is expanded sufficiently to separate the conductors opening a signal circuit. Filling of the reservoir and consequent expansion of the resilient walls places them in tension generating a low residual pressure in the fluid system. This pressure acts to provide a constant low-pressure leak test of the system as it will force the fluid outwardly through any leakage passages. Should a loss of fluid occur, the resilient reservoir material contracts engaging the conductors energizing the signal circuit. One form of embodiment includes blade-type conductors engaging both upon the occurrence of sufficient expansion and contraction of the reservoir completing a circuit indicating overfilled or underfilled conditions.

United States Patent 72] Inventor Ronald L. Shellhause Primary Examiner-Alvin l-l. Waring Vandalia, Ohio Assistant ExaminerGlen R. Swann, Ill 2 A L N 836,238 Attorneys-Frank J. Soucek and Charles R. Engle [22] Filed June 25, 1969 [45] Patented Apr. 6, 1971 [73] Assignee General Motors Corporation Detroit, Mich.

ABSTRACT: A fluid accumulator reservoir includin metallic [54] g sfig RESERVOIR WITH conductors slidably embedded within the resilient wills defin- 5 Claims 9 Drawing Figs v mg the reservo r, the conductors being posit oned to indicate whether a desired amount of fluid exists in the reservoir. [52] US. Cl 340/60, w the reservoir is propefly fill d the resilient material is 188/1, 200/83, 340/5 expanded sufficiently to separate the conductors opening a Int. ignal circuit of the reservoir and consequent expanof Search ign of the resilient walls places them in tension generating a (C), 52 (F), 5&200/61- (25), (26) low residual pressure in the fluid system. This pressure acts to 81(8) 81(2); 188/ l (A) provide a constant low-pressure leak test of the system as it will force the fluid outwardly throu h any leakage assa es. [561 References and Should a loss of fluid occur, the re silient reservoir mate rial UNITED STATES PATENTS contracts engaging the conductors energizing the signal cir- 2,725,434 1 1/1955 Brodsky 200/61.(26) cuit. One form of embodiment includes blade-type conductors 2,969,824 1/1961 Howard..... 200/61.(25) engaging both upon the occurrence of sufficient expansion 3,251,032 5/1966 Brayton..... 340/60 and contraction of the reservoir completing a circuit indicat- 3,42l,322 1/1969 Reznicek 340/60( UX) ing overfilled or underfilled conditions.

Patented April 6, 1971 3,573,725

2 Sheets-Sheet 1 x) TTORNEY RESILIENT ACCUMULATOR RESERVOIR WITH FAILURE SWITCH BACKGROUND OF THE INVENTION Many vehicle brake fluid level-indicating systems are in existence and a specific embodiment of this invention relates to an improvement thereof. Heretofore, various means have been employed to inform the operator of loss of brake fluid in the brake master cylinder. These arrangements usually involve relatively complicated structures or the utilization of magnets in association with switch contacts which require serious consideration during the manufacture of the master cylinder assembly. Insulation of these switches in conjunction with movement of the magnets often becomes relatively complicated. It is, therefore, a purpose of this invention to provide a reliable and simple means for providing a signal should a loss of brake fluid occur. This purpose is accomplished by molding or otherwise slidably placing blade-type switch conductors within elastic material defining a fluid accumulator, whereby the conductors open and close in response to expansion and contraction of the elastic material responsive to the quantity of fluid present in the accumulator.

SUMMARY OF THE INVENTION Accordingly a first object of this invention is the provision of an insulated switch assembly composed of a minimum number of parts and being responsive to the quantity of fluid in the reservoir.

A further object of this invention is the provision of a master cylinder assembly including a fluid failure switch which is completely isolated from the hydraulic brake fluid, thereby preventing objectionable electrochemical erosion of the master cylinder parts.

A still further object of this invention is the provision of a switch assembly including elements slidably embedded within the elastic material forming a resilient accumulator which are movable between opened and closed positions in response to the prevailing quantity of fluid within the accumulator as the elastic material slidable expands and contracts relative to the switch elements.

Another object of this invention is the provision of a fluid responsive switch assembly which is simultaneously assembled to a master cylinder body while securing a resilient accumulator reservoir thereto.

Yet another object of this invention is the provision of a vehicle brake master cylinder assembly including a fluid failure switch having components disposed within the elastic material forming a fluid reservoir wherein the contacts of the switch assembly are simultaneously secured for connection to a signal circuit when the reservoir material is secured to the brake master cylinder body.

A further object of this invention includes the provision of a switch assembly including elements positioned within the elastic walls of an accumulator reservoir, wherein the switch elements engage upon sufficient expansion of the material to indicate an overfilled condition and also engage upon contraction of the material to indicate an underfilled condition.

A still further object of this invention is the provision of a resilient wall accumulator wherein the resilient wall is expanded in tension when the accumulator is filled with fluid, the tension force of the wall slightly pressurizing the fluid-preloading piston cup or the like seals into conformance with cylinder wall irregularities while also providing a constant lowpressure system leak test.

IN THE DRAWINGS FIG. I is a cross-sectional elevational view of a dual resilient accumulator reservoir vehicle master cylinder made in accordance with the subject invention.

FIG. 2 is a fragmentary sectional view of FIG. 1, illustrating a lower portion of one of the accumulator reservoirs filled with fluid slidably expanding the resilient wall relative to the disengaged switch conductors.

FIG. 3 is a fragmentary sectional view of a portion of a resilient accumulator reservoir showing the reservoir wall in a contracted loss of fluid condition drawing the conductors into an engaged switch closed position.

FIG. 4 is a perspective view illustrating a preferred form of the switch elements utilized in this invention.

FIG. 5 is a fragmentary sectional view of a lower portion of a filled resilient accumulator master cylinder reservoir, wherein the reservoir wall slidably contains modified switch elements.

FIG. 6 is a partial fragmentary view of FIG. 5 taken on lines 6 illustrating the modified switch contacts in an open position.

FIG. 7 illustrates the contacts of FIG. 6 in a reservoir wall contracted switch closed position.

FIG. 8 illustrates the switch contacts of FIG. 6 in a reservoir wall expanded switch closed position.

FIG. 9 is a perspective view of the modified switch contacts illustrated in FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A dual master cylinder 10, shown in FIG. 1, includes annular resilient accumulators l2 and 14 which are mounted upon a metallic cylinder body 16. The accumulators include elastic material walls 13 and 15. The cylinder body 16 contains a cylindrical bore 18 receiving brake-actuating pistons 20 and 22 which are respectively biased to retracted positions by springs 24 and 26. A floating piston 23 is centrally disposed in bore 18 to maintain the pistons 20,22 and springs 24,26 in an operative relationship. The piston 20 is biased against a slidable block 28 by the spring 24, the block 28 being engaged by one end of a brake-actuating push rod 30. The resilient accumulators l2 and 14 are secured to body 16 by means of spring biased n'ng clamps 32 engaging accumulator flange portions 34 and 36 to form a fluidtight seal between the accumulators and body 16 thereby defining fluid reservoirs 38 and 40. Accumulators l2 and I4 contain needle valve ports 42 and 44 for supplying make up fluid to the reservoirs 38 and 40.

Actuation of the push rod 30 against block 28 moves it and piston 20 against the force of spring 24 pressurizing fluid in chamber 46 while piston 22 is moved pressurizing fluid in a chamber 48, thereby applying the front and rear vehicle wheel brakes. Flow operated compensating valve assemblies 50 are provided to control the fluid between reservoirs 38 and 40 and the pressure chambers 46 and 48, respectively, so that the system is automatically made up with fluid as required.

Referring now to FIG. 2, a lower portion of accumulator 12 is shown being attached to master cylinder body 16 by the aforementioned clamping rings 32 to define the annular fluid reservoir 38 about cylinder 16. Since the accumulators 12 and 14 are identical in form, only a lower portion of accumulator 12 is shown in FIG. 2 for descriptive purposes. A rubber resilient composition or other elastic fluid resistant material can be used to form wall 13 of the accumulator 12. This elastic wall 13 slidably contain flexible strip or blade-type metallic electrical conductors 52 forming a switch assembly responsive to the amount of fluid present in reservoir 38. The accumulator wall 13 freely expands and contracts relative to the conductors 52 with changes in quantity of fluid present in reservoir 38. The conductors 52 terminate in bulbous bentover contacts 54 which are best illustrated in FIG. 4. The accumulator 12, in a preferred form, is molded to include narrow tunnel cavities 56 for the respective receipt of the conductors and their associated contacts. The bulbous contacts 54 stretch the wall 13 to form a somewhat larger central cavity 58 in the cavities 56 when the accumulator is filled with fluid as in FIG. 2. Tension of wall 13 applies a force against the contacts 54 normal to their line of movement, this force being utilized for a purpose later described. It is apparent that the conductors 52 may be placed within the elastic walls in any fashion, such as by providing a laminated construction of the wall 13 with the conductive members placed between the laminations. It is also apparent the conductors can take any form as long as they are sufficiently stiff and resilient for the wall to expand and contract and actuate them into and out of switching engage ment. In FIG. 3, the reservoir is shown completely empty of fluid with the wall 13 being contracted engaging the contacts 54 in an overlapped electrically connected position. As previously mentioned tension of the wall 13 presses contacts 54 into engagement assuring a positive circuit connection as evidenced by the central cavity 58 decreasing to a length only sufficient to contain the contacts.

Modified metallic strip conductors 62 and 64 are incorporated in the assembly shown in FIG. 5 and are illustrated in detail in FIGS. 6 through 9. Conductor 62 is formed with a contact arm 66 extending axially therefrom at a slightly offcenter position, the arm 66 temiinating in a laterally extending contact 68. Associated conductor 64 has a similarly extending contact arm 70 extending axially toward strip 62 and terminating in a laterally extending contact 72. The conductors 62 and 64 comprise end surfaces 74 and 76 with the contact 68 being reciprocally located between contact 72 and end surface 76, while contact 72 is reciprocally located between contact 68 and end surface 74, as shown in H6. 6. In this arrangement, sufiicient contraction of wall 13, forming accumulator 12', engages contact68 with end surface 76 while contact 72 engages end surface 74 completing a circuit through the conductors 62 and 64 to a signalling device, as shown in FIG. 7. As illustrated in FIG. 8, sufficient expansion of wall l3 engages the contacts 68 and 72 also energizing the signalling circuit indicating reservoir overfilling. ln this situation the reservoir can then be slightly drained to open the signal circuit while maintaining a desired fluid supply for the vehicle brake system. With regard to the signal circuit one of the conductors S2 in each of the accumulators l2 and 14 is grounded to cylinder body 16 at 74, while the other conductor is connected to an electrical lead 76 in series with signal light 78 and a DC source 80, the source 80 being grounded at 82.

From the above description it is obvious that a loss of fluid in either or both of the reservoirs 38 or 40 causes at least one set of contacts 54 to close and energize the light 80. The circuitry can readily be adapted to a single reservoir fluid system by merely connecting the light 78 and source 80 in series with the ground connection 82.

It is significant that the elastic walls 13 and are placed in tension when the reservoirs 38 and 40 contain fluid. In the case of the overlapped contacts 54 shown in H6. 3, this tension force assures a positive switch closed engagement of the contacts. Additionally, the tension of the walls creates a low residual fluid pressure in the system. This pressure, of course, will vary with the amount of fluid in the reservoirs, however, if the vehicle brake system contains enough fluid to be functional, the pressure is sufficient to expand and preload the cup seals of pistons 20 and 22 into relatively tight conformance with the walls of bore 18. This low residual fluid pressure also serves as a constant leak test as it causes the fluid to continually seek an exit from the system. Should a leak exist, the low residual pressure forces the fluid from the system and the walls 13 and 15 contract closing contacts 54 to complete the warning signal circuit shown in FIG. 2.

This invention provides a reliable switching arrangement that can readily be connected in a signalling circuit indicating a loss of fluid and with use of one form of the switching assembly also indicate an overfilled condition. The resilient accumulators are shown in conjunction with a vehicle brake system for purposes of description only, it being apparent that the signalling arrangement is capable of being used with any fluid system including a resilient reservoir.

lclaim:

1. In a fluid accumulator assembly of the type employing an expandable and contractable resilient member forming a reservoir, the improvement comprising: a first electrically conductive member slidably embedded within said annular resilient member, said first conductive member having a secured end and a freely extending end, a second conductive member slidably embedded within said resilient member, said second conductive member having a secured end and a free end extending toward but being spaced from said first conductive member free end in said cavity when said reservoir is expanded, and circuit means connected to the secured ends of said conductive members, the occurrence of a sufficient loss of reservoir fluid contracting said resilient member so as to slide the conductive members within the resilient member to engage the free ends thereof completing the circuit to a signalling device.

2. In a fluid accumulator of the type including a resilient annular member being secured to a body member and defining a fluid reservoir thereabout, the improvement comprising: a first electrically conductive member slidably embedded within the resilient member having a secured end and a free end extending toward the intermediate portion of said annular member; a second conductive member having a secured end and a free end extending toward the free end of said first conductive member, the free end of said first conductive member terminating in an end surface having a relatively narrow centrally offset axially extending member, said axially extending member terminating in a first laterally extending contact; the free end of said second contact member terminating in an end surface having a relatively narrow centrally offset axially extending member, said axially extending member terminating in a second laterally extending contact, said axially extending members being positioned to overlap one another such that sufficicnt expansion of said annular member engages said lateral contacts, contraction of said resilient annular member causing said first and second lateral contacts, respectively, to engage the terminal end surfaces of said second and first conductive members; and circuit means connected to the respective secured ends of said conductive members being energized when said lateral contacts engage indicating expansion of said annular member and being energized when said lateral contacts engage said end surfaces indicating contraction of said annular member.

3. In a vehicle dual master cylinder assembly including a body member containing a cylindrical bore; a pair of pressurizing pistons slidably operable within the bore; a brake applying push rod actuating said pistons supplying pressurized fluid separately to front and rear vehicle brake systems during application of the brakes; a pair of resilient annular members clamped to said body member and forming separate annular reservoirs about said body member, said reservoirs supplying makeup fluid to the separate brake systems as required; the improvement comprising: a first electrically conductive strip member slidably embedded within one of said resilient annular members and having one end simultaneously clamped to said body member with one side of said one resilient annular member, said first conductive strip member having a free end extending toward a central cavity in said one annular member; a second electrically conductive strip member having one end clamped to said body member simultaneously with the other side of said one annular member and also having a free end extending toward the free end of said first strip member normally being spaced therefrom, said second conductive strip member also being slidably embedded within said one resilient member, a third electrically conductive strip member slidably embedded within the other of said annular members and having one end clamped simultaneously with one side of said other annular member to said master cylinder body member, a fourth electrically conductive strip member also slidably embedded within the other of said annular members having one end clamped simultaneously with the other side of said other annular member to said master cylinder body member, said third conductive member having a free end extending toward a free end of said fourth strip member normally being spaced therefrom, and electrical circuit means attached to said clamped ends of said strip members, said circuit means including a signalling device whereby contraction of one of said annular members moves the free ends of its embedded conductive strip members into engagement closing said circuit means energizing said signalling device indicating a loss of fluid in the one annular member and contraction of the other annular member moves its conductive strip member free ends into engagement closi'ng said circuit means indicating a loss of fluid in the other of said reservoirs.

4 In a fluid accumulator assembly of the type employing an annular expandable and contractable resilient member having elastic walls forming a reservoir, the improvement comprising: a first electrically conductive member slidably embedded within said elastic walls, said first conductive member having a secured end and a freely extending end, a second conductive member slidably embedded within said elastic walls, said second conductive member having a secured end and a free end extendingtoward but being spaced from said first conductive member free end when said walls are expanded, and circuit means connected to the secured ends of said conductive members, the occurrence of a suflicient loss of reservoir fluid contracting said walls and a slidably engaging the free ends of said conductive members within the elastic walls completing the circuit to a signalling device, expansion of said walls placing them in sufficient tension to generate a low residual fluid pressure in the assembly, said fluid pressure providing a constant system leak test.

5. in a vehicle brake system including a master cylinder comprising a body member, an expansible and contractable annular elastic member defining a reservoir secured to said body member, a switch assembly including contacts movable between open circuit and closed circuit positions, said switch assembly being actuated by said annular member to a circuit open position when said annular member contains fluid and is expanded, said switch assembly being actuated by said annular member to a circuit closed position when said annular member is empty of fluid and is contracted, and a warning signal circuit connected to said switch assembly informing the operator of a loss of fluid when said annular member contracts closing said switch, expansion of said annular member by fluid contained therein placing said elastic member in tension, the tension force reacting to generate a low residual fluid pressure in said reservoir and said brake system, said fluid pressure to provide a constant leak test of the system and to preload fluid seals seals into engagement with mating surfaces. 

1. In a fluid accumulator assembly of the type employing an expandable and contractable resilient member forming a reservoir, the improvement comprising: a first electrically conductive member slidably embedded within said annular resilient member, said first conductive member having a secured end and a freely extending end, a second conductive member slidably embedded within said resilient member, said second conductive member having a secured end and a free end extending toward but being spaced from said first conductive member free end in said cavity when said reservoir is expanded, and circuit means connected to the secured ends of said conductive members, the occurrence of a sufficient loss of reservoir fluid contracting said resilient member so as to slide the conductive members within the resilient member to engage the free ends thereof completing the circuit to a signalling device.
 2. In a fluid accumulator of the type including a resilient annular member being secured to a body member and defining a fluid reservoir thereabout, the improvement comprising: a first electrically conductive member slidably embedded within the resilient member having a secured end and a free end extending toward the intermediate portion of said annular member; a second conductive member having a secured end and a free end extending toward the free end of said first conductive member, the free end of said first conductive member terminating in an end surface having a relatively narrow centrally offset axially extending member, said axially extending member terminating in a first laterally extending contact; the free end of said second contact member terminating in an end surface having a relatively narrow centrally offset axially extending member, said axially extending member terminating in a second laterally extending contact, said axially extending members being positioned to overlap one another such that sufficient expansion of said annular member engages said lateral contacts, contraction of said resilient annular member causing said first and second lateral contacts, respectively, to engage the terminal end surfaces of said second and first conductive members; and circuit means connected to the respective secured ends of said conductive members being energized when said lateral contacts engage indicating expansion of said annular member and being energized when said lateral contacts engage said end surfaces indicating contraction of sAid annular member.
 3. In a vehicle dual master cylinder assembly including a body member containing a cylindrical bore; a pair of pressurizing pistons slidably operable within the bore; a brake applying push rod actuating said pistons supplying pressurized fluid separately to front and rear vehicle brake systems during application of the brakes; a pair of resilient annular members clamped to said body member and forming separate annular reservoirs about said body member, said reservoirs supplying makeup fluid to the separate brake systems as required; the improvement comprising: a first electrically conductive strip member slidably embedded within one of said resilient annular members and having one end simultaneously clamped to said body member with one side of said one resilient annular member, said first conductive strip member having a free end extending toward a central cavity in said one annular member; a second electrically conductive strip member having one end clamped to said body member simultaneously with the other side of said one annular member and also having a free end extending toward the free end of said first strip member normally being spaced therefrom, said second conductive strip member also being slidably embedded within said one resilient member, a third electrically conductive strip member slidably embedded within the other of said annular members and having one end clamped simultaneously with one side of said other annular member to said master cylinder body member, a fourth electrically conductive strip member also slidably embedded within the other of said annular members having one end clamped simultaneously with the other side of said other annular member to said master cylinder body member, said third conductive member having a free end extending toward a free end of said fourth strip member normally being spaced therefrom, and electrical circuit means attached to said clamped ends of said strip members, said circuit means including a signalling device whereby contraction of one of said annular members moves the free ends of its embedded conductive strip members into engagement closing said circuit means energizing said signalling device indicating a loss of fluid in the one annular member and contraction of the other annular member moves its conductive strip member free ends into engagement closing said circuit means indicating a loss of fluid in the other of said reservoirs.
 4. In a fluid accumulator assembly of the type employing an annular expandable and contractable resilient member having elastic walls forming a reservoir, the improvement comprising: a first electrically conductive member slidably embedded within said elastic walls, said first conductive member having a secured end and a freely extending end, a second conductive member slidably embedded within said elastic walls, said second conductive member having a secured end and a free end extending toward but being spaced from said first conductive member free end when said walls are expanded, and circuit means connected to the secured ends of said conductive members, the occurrence of a sufficient loss of reservoir fluid contracting said walls and a slidably engaging the free ends of said conductive members within the elastic walls completing the circuit to a signalling device, expansion of said walls placing them in sufficient tension to generate a low residual fluid pressure in the assembly, said fluid pressure providing a constant system leak test.
 5. In a vehicle brake system including a master cylinder comprising a body member, an expansible and contractable annular elastic member defining a reservoir secured to said body member, a switch assembly including contacts movable between open circuit and closed circuit positions, said switch assembly being actuated by said annular member to a circuit open position when said annular member contains fluid and is expanded, said switch assembly being actuated by said annular member to a circuit closed position when said annular member is empty of fluid and is contracted, and a warning signal circuit connected to said switch assembly informing the operator of a loss of fluid when said annular member contracts closing said switch, expansion of said annular member by fluid contained therein placing said elastic member in tension, the tension force reacting to generate a low residual fluid pressure in said reservoir and said brake system, said fluid pressure to provide a constant leak test of the system and to preload fluid seals seals into engagement with mating surfaces. 